WDH Bars Close to Max Rating

Depends on how much work they have to do to keep things level. With a 2500HD truck, They're not going to need as much tension as on a lightly sprung half ton. I use 800# bars on my Reese DC for our 850-900~lb tongue weight as the truck barely settles two inches. I use the full length of chain to bring the rear back up one inch. Tows and rides good.

Since you already have them, try the 800# bars first. If you are able to transfer enough weight with them that you don't have any significant sag at the back of the TV or sway when driving, keep them.
I once had over sized bars and had a difficult time adjusting them. They wanted to make the front of the TT and the back of the truck bounce over every little bump.
Doesn't hurt to try them first.

Obviously you are trying to err on the side of caution or you would not be thinking about this, and I would tend to agree with you, Go to the stiffer bars as you aproach the change point, You have to assume that over time they lose at least a little of their tension so a little overkill shouldnt hurt.